The present invention is concerned with coagulation-neutral, hydrophilic glass fibres, a process for the production thereof and an agent for the separation of plasma from blood.
European patent specification No. 00 45 476 describes agents and processes for the separation of plasma or serum from whole blood which make it possible to determine component materials from whole blood in a simple way. According to this patent specification, the plasma can be separated from the erythrocytes by allowing whole blood to run through a layer of glass fibres with fibre diameters of less than 2.5.mu., the glass fibres holding back the erythrocytes. The blood is preferably applied to one end of a rectangular glass fibre fleece, from whence the plasma is transported capillarily into the other region. There is then pressed onto the part of the fleece filled with plasma, a matrix (paper, absorbent film, etc.) containing the reagents needed for a detection reaction for the parameter to be determined via measurements of diffuse reflectivity.
This simple plasma obtaining and plasma transport system can be used for all clinical-chemically important parameters with the exception of parameters which are to be determined in the scope of the investigations of haemostasiological questions. It is known that coagulation analyses are carried out in synthetic resin vessels or glass vessels which are inactivated by a coating of silicone resin because untreated glass influences the coagulatability of blood or plasma. Thus, by activation, glass shortens the Prothrombin time of plasmas having coagulation factors which lie in the normal range. The Prothrombin time is prolonged in the case of low percentage plasmas by inactivation of coagulation factors. Glass inactivates, in particular, Factors V and IIa. Due to this inactivation and thus falsely prolonged Prothrombin time, the diagnostic use is destroyed because the ratios of the individual coagulation factors are displaced. The Prothrombin time value given as a percentage (Quick %) includes the fibrinogen concentration and the activity of Factors II, V, VII and X. A pool plasma from healthy donors is defined as 100% plasma and, by way of dilution with physiological saline, corresponding lower percentage plasmas are prepared. By means of this dilution series, a reference curve is produced on the basis of which the Prothrombin time values for patients' plasmas are determined.
However, the determination of the activated partial thromboplastin time (PTT) is also negatively influenced by the inactivation of Factors XII and XI. The detection of anti-thrombin III and heparin is considerably disturbed by an inactivation of thrombin by glass.
Therefore, it is an object of the present invention to modify the separation and transport systems according to European patent specification No. 00 45 476 so that they become coagulation-neutral without changing their separation and transport properties so that they can also be used for haemostasiological investigations.
A possible solution to the above problems is to use fibre materials made from synthetic resins. However, with regard to their separation behaviour towards the erythrocytes, these fibre materials do not have the desired properties and, in part, considerably influence the coagulatability of plasmas. It is also known that glasses can be superficially coated by siliconization with silicone resin emulsions to exclude the influencing of the coagulation factors thereby. However, this siliconization brings about, in the special case of the glass fibres, such a strong hydrophobing of the surface that wetting can no longer take place and thus the fibres completely lose their erythrocyte separation and plasma transport properties.